Grain refining aluminium foundry alloys with commercial Al-B master alloys

In Al-3B master alloy, a higher fraction of borides is of the AlB2 variety, while in Al-8B alloy, the predominant species is the AlB12 phase. AlB12 is less stable than AlB2 and is engaged in exchange reactions, leading to the formation of transition metal diborides that subsequently settle at the bottom of the melt. Hence, AlB12 is involved more in precipitating transition elements than in refining the grain structure. With predominantly AlB12 particles, Al-8B master alloys are better suited for the removal of transition metal impurities in the manufacture of aluminium conductors. Al-3B, on the other hand, is a better grain refiner as the majority of its borides are of the AlB2 variety. Which of the two master alloys is used in grain refinement does not make a difference once the transition metal impurities have been precipitated. B is dedicated to grain refinement in an impurity free aluminium melt and produces exceptionally small equiaxed grains across the section of the samples.